For other clearly wrong, or wrongly interpreted information: While 70% of the population is lactose intolerant, that doesn't mean you are. We do know that about 99% of the Chinese population is lactose intolerant (which proooobably skews the numbers a bit), yet, for example, only about 1% of Dutch people are lactose intolerant. Northern Europeans and other people from historically very dairy-rich cultures have a very high degree of lactose tolerance, and persistent lactase production (the enzyme that digests lactose and makes you lactose tolerant). Very interesting genetics topic :) Statistics will not say anything useful about whether you are likely to be lactose intolerant, but ethnicity will. Get tested if you are in doubt. It's a simple test. Just make sure you go to a qualified medical practitioner.
As for gluten insensitivity, this is called coeliac disease and is very serious. Thankfully, the highest estimate for prevalence is about 1%, not 15%. The anti-gluten brigade has been on it for years, but non-coeliac people can and should eat gluten. It's a good protein of high quality and makes your bread dough stick together. That's why it's hell trying to bake gluten-free bread or pizza dough.
Casein, a milk protein, is also not a bad protein. While there are many scare stories about casein (it being blamed for autism, cancer, et cetera), they don't hold up very well. Casein is a nice, slow-digesting protein with a very good quality, as any body builder who does the diet/protein thing will be able to tell you. Drink your milk if you can tolerate it, and eat more cheese :)
As for multiple sclerosis, we actually don't know what causes it other than that there likely is a genetic component, but that other factors also interfere. For the actual, REAL long term effects of coeliac disease, see here: http://celiacdisease.about.com/od/symptomsofceliacdisease/a/...
As for cortisol, your body regulates this itself. If you're stressed, stress down. But if your body doesn't regulate itself, you have a huge problem and need to see a doctor right away.
While "eat food, not too much, mostly plants" is very good advice, there's also another piece of advice that has been forgotten: "You are probably not sick, and your body can take care if it." Just eat a normal, healthy diet.
Man. That was long. Sorry about that, but I had to get some facts out.